Many behaviors can be described in terms of the interaction and coordination of reflexive and "command" neuronal activity. Although both kinds of behavior have proven amenable to analysis at the cellular level, little is know about the mechanisms of interaction between them. The escape swimming behavior of the marine mollusc,Tritonia diomedia, provides an exceptional preparation in which to investigate the principles of neuronal organization underlying the generation of relatively complex behaviors. Swimming consists of a reflexive withdrawal followed by a sequence of strictly alternating ventral and dorsal flexions. The mechanism of generating motoneuronal activity "switches" from reflexogenic to preprogrammed. The basic questions are to be studied. What, at the cellular level, is the mechanism of "switching" from reflexogenic to command motoneuronal activity? What is the effect of the "switching" process on the integration of sensory input to the reflexive and command pathways? Using a whole animal preparation capable of normal behavior, the processing of relevant sensory input mediating reflexive withdrawals and the initiation of preprogrammed swimming will be mapped by intracellular recording from identified central neurons. A new desheathing procedure and the resulting identification of central sensory cells has opened the way for a comprehensive analysis of the neuronal circuitry from sensory receptors to motoneurons mediating escape swimming.